The earlier types of materials employed for correcting errors on a typed page were gum erasers. The ink composition on the typewriter ribbon in use at that time was absorbed into the paper and attempts at erasure of a typed character often resulted in tearing the paper on which the error was typed. The development of nonabsorbent ink compositions of transfer materials which did not wet or dye the paper onto which typed images are printed made it possible to remove erroneously typed characters with an adhesive.
A useful known method to correct erroneously typed images is to provide in a typewriter, such as that designed as the Correcting Selectric.RTM. typewriter model manufactured by International Business Machines Corporation, a typing operation and a pressure sensitive adhesive ribbon which can be fed by such feed mechanism to supplant the ribbon for a correction operation. In this type of operation, the erroneous image is overstruck using the appropriate type or key. The pressure sensitive ribbon is retained, spaced from the copy sheet to be corrected except in impressed areas which adhere to the erroneously typed image and lift the erroneously typed image from the substrate when typing pressure is released. Thereafter, the correct image is typed in place of the removed erroneously typed image. As referred to above, this type of operation is especially used in association with imaging compositions which are dry and are substantially free from oils and free from dissolved dyes which can migrate into the substrate and stain the paper fibers.
Although such pressure sensitive correction ribbons are in current commercial use, they do present some crucial problems. For instance, many of the commercially available pressure sensitive ribbon compositions tend to stick to the transfer ribbon, to the ribbon guides, and card holder, which is undesirable from the standpoint of effectively and efficiently operating a typewriter. Moreover, certain feed problems exist due to the high take-up and unwind tension necessary with the ribbons now commercially available. Furthermore, in view of the adhesive characteristics of the presently known correction tapes, picking up of paper fibers during correction occurs sometimes. Also, coning and telescoping of unwound spools can occur when employing presently available lift-off correction ribbons.
Many of the presently available compositions suggested for pressure sensitive materials for removing erroneous type either involve the use of relatively large amounts of inert, finely divided fillers, such as titanium dioxide, in order to reduce the surface tack, or include the use of a sticky adhesive layer in combination with a passive surface layer over the sticky layer. The sticky layer is activated with application of typing pressure. Those compositions which require the use of a tacky adhesive layer and a passive boundary layer involve more elaborate and costly methods of preparation.
Those compositions that include the use of large amounts of inert filler material suffer from the disadvantage that the filler material does not impart any adhesive properties to the compositions and, therefore, reduces the overall efficiency of the correction material, the degree of which depends upon the relative amount of filler material employed. In addition, it is often difficult to obtain a uniform dispersion of the filler material throughout the composition which can result in a considerable amount of variation in the performance of the correction material.